I'm trying to determine the most efficient method for a mining project I'm involved with doing with an expansion platform that expands and contracts repeatedly into different substrates (from sandy to gravel to dense muddy material). So whatever design I use will have to be able to open and close quickly and repeatedly even after getting full of muck The expansion area would be roughly oblong to round in shape, about 2 ft. in diameter. I can't go into total detail because of confidentiality agreements I've signed, but would really like some help on efficient ways to accomplish the basic process. What I want to accomplish is have an area expand with a modest amount of pressure on a downward trigger point. I'm thinking a helical screw which simply causes outward rotation of different arms or wings to create a temporarily larger surface area - or maybe a light-weight servo-solenoid switch of some type. But I prefer a strictly mechanical design as much of the usage will be in the field where power may be unavailable. I'm looking for a process that requires as little pressure as possible to initiate the expansion. I am thinking the retraction could be accomplished by simiple torsional or other spring process. Thanks for any ideas!